Internal combustion engines (e.g., diesel engines) typically generate an exhaust flow that contains varying amounts of particulate matter (PM). The amount and size distribution of particulate matter in the exhaust flow tends to vary with engine operating conditions, such as fuel injection timing, injection volume, injection pressure, or the engine speed to load relationship. Adjustment of these conditions may be useful in reducing particulate matter emissions and average particle size of the particulate matter from the engine. Reducing particulate matter emissions from internal combustion engines is environmentally favorable. In addition, particulate matter measurements for diesel exhaust is useful for on-board (e.g., mounted on a vehicle) diagnostics of PM filters and reduction of emissions through combustion control.
Conventional technologies that may be used for on-board monitoring of particulate matter in exhaust flow include the use of wire electrodes in sensor applications. Wire electrode sensors apply a high voltage between two electrodes and measure the current or charge between the electrodes. The electrode measurement is correlated with a specific particulate matter concentration. However, wire electrode sensors are subject to the de-calibration and baseline drift of the sensor due to accumulation of soot (i.e., particulate matter deposit) on and between the electrodes. Wire electrodes are also subject to vibration, which changes the distance between the electrodes. As the distance between the electrodes changes according to the vibration of the electrodes, the varying distance introduces error in the particulate matter reading.